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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2006 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.util.concurrent;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import static com.google.common.base.Preconditions.checkArgument;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import static com.google.common.base.Preconditions.checkNotNull;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import static com.google.common.base.Preconditions.checkState;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import static com.google.common.util.concurrent.MoreExecutors.sameThreadExecutor;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import static com.google.common.util.concurrent.Uninterruptibles.getUninterruptibly;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import static java.lang.Thread.currentThread;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import static java.util.Arrays.asList;<a name="line.25"></a>
<span class="sourceLineNo">026</span><a name="line.26"></a>
<span class="sourceLineNo">027</span>import com.google.common.annotations.Beta;<a name="line.27"></a>
<span class="sourceLineNo">028</span>import com.google.common.base.Function;<a name="line.28"></a>
<span class="sourceLineNo">029</span>import com.google.common.base.Optional;<a name="line.29"></a>
<span class="sourceLineNo">030</span>import com.google.common.base.Preconditions;<a name="line.30"></a>
<span class="sourceLineNo">031</span>import com.google.common.collect.ImmutableCollection;<a name="line.31"></a>
<span class="sourceLineNo">032</span>import com.google.common.collect.ImmutableList;<a name="line.32"></a>
<span class="sourceLineNo">033</span>import com.google.common.collect.Lists;<a name="line.33"></a>
<span class="sourceLineNo">034</span>import com.google.common.collect.Ordering;<a name="line.34"></a>
<span class="sourceLineNo">035</span><a name="line.35"></a>
<span class="sourceLineNo">036</span>import java.lang.reflect.Constructor;<a name="line.36"></a>
<span class="sourceLineNo">037</span>import java.lang.reflect.InvocationTargetException;<a name="line.37"></a>
<span class="sourceLineNo">038</span>import java.lang.reflect.UndeclaredThrowableException;<a name="line.38"></a>
<span class="sourceLineNo">039</span>import java.util.Arrays;<a name="line.39"></a>
<span class="sourceLineNo">040</span>import java.util.List;<a name="line.40"></a>
<span class="sourceLineNo">041</span>import java.util.concurrent.CancellationException;<a name="line.41"></a>
<span class="sourceLineNo">042</span>import java.util.concurrent.CountDownLatch;<a name="line.42"></a>
<span class="sourceLineNo">043</span>import java.util.concurrent.ExecutionException;<a name="line.43"></a>
<span class="sourceLineNo">044</span>import java.util.concurrent.Executor;<a name="line.44"></a>
<span class="sourceLineNo">045</span>import java.util.concurrent.Future;<a name="line.45"></a>
<span class="sourceLineNo">046</span>import java.util.concurrent.TimeUnit;<a name="line.46"></a>
<span class="sourceLineNo">047</span>import java.util.concurrent.TimeoutException;<a name="line.47"></a>
<span class="sourceLineNo">048</span>import java.util.concurrent.atomic.AtomicInteger;<a name="line.48"></a>
<span class="sourceLineNo">049</span>import java.util.logging.Level;<a name="line.49"></a>
<span class="sourceLineNo">050</span>import java.util.logging.Logger;<a name="line.50"></a>
<span class="sourceLineNo">051</span><a name="line.51"></a>
<span class="sourceLineNo">052</span>import javax.annotation.Nullable;<a name="line.52"></a>
<span class="sourceLineNo">053</span><a name="line.53"></a>
<span class="sourceLineNo">054</span>/**<a name="line.54"></a>
<span class="sourceLineNo">055</span> * Static utility methods pertaining to the {@link Future} interface.<a name="line.55"></a>
<span class="sourceLineNo">056</span> *<a name="line.56"></a>
<span class="sourceLineNo">057</span> * &lt;p&gt;Many of these methods use the {@link ListenableFuture} API; consult the<a name="line.57"></a>
<span class="sourceLineNo">058</span> * Guava User Guide article on &lt;a href=<a name="line.58"></a>
<span class="sourceLineNo">059</span> * "http://code.google.com/p/guava-libraries/wiki/ListenableFutureExplained"&gt;<a name="line.59"></a>
<span class="sourceLineNo">060</span> * {@code ListenableFuture}&lt;/a&gt;.<a name="line.60"></a>
<span class="sourceLineNo">061</span> *<a name="line.61"></a>
<span class="sourceLineNo">062</span> * @author Kevin Bourrillion<a name="line.62"></a>
<span class="sourceLineNo">063</span> * @author Nishant Thakkar<a name="line.63"></a>
<span class="sourceLineNo">064</span> * @author Sven Mawson<a name="line.64"></a>
<span class="sourceLineNo">065</span> * @since 1.0<a name="line.65"></a>
<span class="sourceLineNo">066</span> */<a name="line.66"></a>
<span class="sourceLineNo">067</span>@Beta<a name="line.67"></a>
<span class="sourceLineNo">068</span>public final class Futures {<a name="line.68"></a>
<span class="sourceLineNo">069</span>  private Futures() {}<a name="line.69"></a>
<span class="sourceLineNo">070</span><a name="line.70"></a>
<span class="sourceLineNo">071</span>  /**<a name="line.71"></a>
<span class="sourceLineNo">072</span>   * Creates a {@link CheckedFuture} out of a normal {@link ListenableFuture}<a name="line.72"></a>
<span class="sourceLineNo">073</span>   * and a {@link Function} that maps from {@link Exception} instances into the<a name="line.73"></a>
<span class="sourceLineNo">074</span>   * appropriate checked type.<a name="line.74"></a>
<span class="sourceLineNo">075</span>   *<a name="line.75"></a>
<span class="sourceLineNo">076</span>   * &lt;p&gt;The given mapping function will be applied to an<a name="line.76"></a>
<span class="sourceLineNo">077</span>   * {@link InterruptedException}, a {@link CancellationException}, or an<a name="line.77"></a>
<span class="sourceLineNo">078</span>   * {@link ExecutionException}.<a name="line.78"></a>
<span class="sourceLineNo">079</span>   * See {@link Future#get()} for details on the exceptions thrown.<a name="line.79"></a>
<span class="sourceLineNo">080</span>   *<a name="line.80"></a>
<span class="sourceLineNo">081</span>   * @since 9.0 (source-compatible since 1.0)<a name="line.81"></a>
<span class="sourceLineNo">082</span>   */<a name="line.82"></a>
<span class="sourceLineNo">083</span>  public static &lt;V, X extends Exception&gt; CheckedFuture&lt;V, X&gt; makeChecked(<a name="line.83"></a>
<span class="sourceLineNo">084</span>      ListenableFuture&lt;V&gt; future, Function&lt;Exception, X&gt; mapper) {<a name="line.84"></a>
<span class="sourceLineNo">085</span>    return new MappingCheckedFuture&lt;V, X&gt;(checkNotNull(future), mapper);<a name="line.85"></a>
<span class="sourceLineNo">086</span>  }<a name="line.86"></a>
<span class="sourceLineNo">087</span><a name="line.87"></a>
<span class="sourceLineNo">088</span>  private abstract static class ImmediateFuture&lt;V&gt;<a name="line.88"></a>
<span class="sourceLineNo">089</span>      implements ListenableFuture&lt;V&gt; {<a name="line.89"></a>
<span class="sourceLineNo">090</span><a name="line.90"></a>
<span class="sourceLineNo">091</span>    private static final Logger log =<a name="line.91"></a>
<span class="sourceLineNo">092</span>        Logger.getLogger(ImmediateFuture.class.getName());<a name="line.92"></a>
<span class="sourceLineNo">093</span><a name="line.93"></a>
<span class="sourceLineNo">094</span>    @Override<a name="line.94"></a>
<span class="sourceLineNo">095</span>    public void addListener(Runnable listener, Executor executor) {<a name="line.95"></a>
<span class="sourceLineNo">096</span>      checkNotNull(listener, "Runnable was null.");<a name="line.96"></a>
<span class="sourceLineNo">097</span>      checkNotNull(executor, "Executor was null.");<a name="line.97"></a>
<span class="sourceLineNo">098</span>      try {<a name="line.98"></a>
<span class="sourceLineNo">099</span>        executor.execute(listener);<a name="line.99"></a>
<span class="sourceLineNo">100</span>      } catch (RuntimeException e) {<a name="line.100"></a>
<span class="sourceLineNo">101</span>        // ListenableFuture's contract is that it will not throw unchecked<a name="line.101"></a>
<span class="sourceLineNo">102</span>        // exceptions, so log the bad runnable and/or executor and swallow it.<a name="line.102"></a>
<span class="sourceLineNo">103</span>        log.log(Level.SEVERE, "RuntimeException while executing runnable "<a name="line.103"></a>
<span class="sourceLineNo">104</span>            + listener + " with executor " + executor, e);<a name="line.104"></a>
<span class="sourceLineNo">105</span>      }<a name="line.105"></a>
<span class="sourceLineNo">106</span>    }<a name="line.106"></a>
<span class="sourceLineNo">107</span><a name="line.107"></a>
<span class="sourceLineNo">108</span>    @Override<a name="line.108"></a>
<span class="sourceLineNo">109</span>    public boolean cancel(boolean mayInterruptIfRunning) {<a name="line.109"></a>
<span class="sourceLineNo">110</span>      return false;<a name="line.110"></a>
<span class="sourceLineNo">111</span>    }<a name="line.111"></a>
<span class="sourceLineNo">112</span><a name="line.112"></a>
<span class="sourceLineNo">113</span>    @Override<a name="line.113"></a>
<span class="sourceLineNo">114</span>    public abstract V get() throws ExecutionException;<a name="line.114"></a>
<span class="sourceLineNo">115</span><a name="line.115"></a>
<span class="sourceLineNo">116</span>    @Override<a name="line.116"></a>
<span class="sourceLineNo">117</span>    public V get(long timeout, TimeUnit unit) throws ExecutionException {<a name="line.117"></a>
<span class="sourceLineNo">118</span>      checkNotNull(unit);<a name="line.118"></a>
<span class="sourceLineNo">119</span>      return get();<a name="line.119"></a>
<span class="sourceLineNo">120</span>    }<a name="line.120"></a>
<span class="sourceLineNo">121</span><a name="line.121"></a>
<span class="sourceLineNo">122</span>    @Override<a name="line.122"></a>
<span class="sourceLineNo">123</span>    public boolean isCancelled() {<a name="line.123"></a>
<span class="sourceLineNo">124</span>      return false;<a name="line.124"></a>
<span class="sourceLineNo">125</span>    }<a name="line.125"></a>
<span class="sourceLineNo">126</span><a name="line.126"></a>
<span class="sourceLineNo">127</span>    @Override<a name="line.127"></a>
<span class="sourceLineNo">128</span>    public boolean isDone() {<a name="line.128"></a>
<span class="sourceLineNo">129</span>      return true;<a name="line.129"></a>
<span class="sourceLineNo">130</span>    }<a name="line.130"></a>
<span class="sourceLineNo">131</span>  }<a name="line.131"></a>
<span class="sourceLineNo">132</span><a name="line.132"></a>
<span class="sourceLineNo">133</span>  private static class ImmediateSuccessfulFuture&lt;V&gt; extends ImmediateFuture&lt;V&gt; {<a name="line.133"></a>
<span class="sourceLineNo">134</span><a name="line.134"></a>
<span class="sourceLineNo">135</span>    @Nullable private final V value;<a name="line.135"></a>
<span class="sourceLineNo">136</span><a name="line.136"></a>
<span class="sourceLineNo">137</span>    ImmediateSuccessfulFuture(@Nullable V value) {<a name="line.137"></a>
<span class="sourceLineNo">138</span>      this.value = value;<a name="line.138"></a>
<span class="sourceLineNo">139</span>    }<a name="line.139"></a>
<span class="sourceLineNo">140</span><a name="line.140"></a>
<span class="sourceLineNo">141</span>    @Override<a name="line.141"></a>
<span class="sourceLineNo">142</span>    public V get() {<a name="line.142"></a>
<span class="sourceLineNo">143</span>      return value;<a name="line.143"></a>
<span class="sourceLineNo">144</span>    }<a name="line.144"></a>
<span class="sourceLineNo">145</span>  }<a name="line.145"></a>
<span class="sourceLineNo">146</span><a name="line.146"></a>
<span class="sourceLineNo">147</span>  private static class ImmediateSuccessfulCheckedFuture&lt;V, X extends Exception&gt;<a name="line.147"></a>
<span class="sourceLineNo">148</span>      extends ImmediateFuture&lt;V&gt; implements CheckedFuture&lt;V, X&gt; {<a name="line.148"></a>
<span class="sourceLineNo">149</span><a name="line.149"></a>
<span class="sourceLineNo">150</span>    @Nullable private final V value;<a name="line.150"></a>
<span class="sourceLineNo">151</span><a name="line.151"></a>
<span class="sourceLineNo">152</span>    ImmediateSuccessfulCheckedFuture(@Nullable V value) {<a name="line.152"></a>
<span class="sourceLineNo">153</span>      this.value = value;<a name="line.153"></a>
<span class="sourceLineNo">154</span>    }<a name="line.154"></a>
<span class="sourceLineNo">155</span><a name="line.155"></a>
<span class="sourceLineNo">156</span>    @Override<a name="line.156"></a>
<span class="sourceLineNo">157</span>    public V get() {<a name="line.157"></a>
<span class="sourceLineNo">158</span>      return value;<a name="line.158"></a>
<span class="sourceLineNo">159</span>    }<a name="line.159"></a>
<span class="sourceLineNo">160</span><a name="line.160"></a>
<span class="sourceLineNo">161</span>    @Override<a name="line.161"></a>
<span class="sourceLineNo">162</span>    public V checkedGet() {<a name="line.162"></a>
<span class="sourceLineNo">163</span>      return value;<a name="line.163"></a>
<span class="sourceLineNo">164</span>    }<a name="line.164"></a>
<span class="sourceLineNo">165</span><a name="line.165"></a>
<span class="sourceLineNo">166</span>    @Override<a name="line.166"></a>
<span class="sourceLineNo">167</span>    public V checkedGet(long timeout, TimeUnit unit) {<a name="line.167"></a>
<span class="sourceLineNo">168</span>      checkNotNull(unit);<a name="line.168"></a>
<span class="sourceLineNo">169</span>      return value;<a name="line.169"></a>
<span class="sourceLineNo">170</span>    }<a name="line.170"></a>
<span class="sourceLineNo">171</span>  }<a name="line.171"></a>
<span class="sourceLineNo">172</span><a name="line.172"></a>
<span class="sourceLineNo">173</span>  private static class ImmediateFailedFuture&lt;V&gt; extends ImmediateFuture&lt;V&gt; {<a name="line.173"></a>
<span class="sourceLineNo">174</span><a name="line.174"></a>
<span class="sourceLineNo">175</span>    private final Throwable thrown;<a name="line.175"></a>
<span class="sourceLineNo">176</span><a name="line.176"></a>
<span class="sourceLineNo">177</span>    ImmediateFailedFuture(Throwable thrown) {<a name="line.177"></a>
<span class="sourceLineNo">178</span>      this.thrown = thrown;<a name="line.178"></a>
<span class="sourceLineNo">179</span>    }<a name="line.179"></a>
<span class="sourceLineNo">180</span><a name="line.180"></a>
<span class="sourceLineNo">181</span>    @Override<a name="line.181"></a>
<span class="sourceLineNo">182</span>    public V get() throws ExecutionException {<a name="line.182"></a>
<span class="sourceLineNo">183</span>      throw new ExecutionException(thrown);<a name="line.183"></a>
<span class="sourceLineNo">184</span>    }<a name="line.184"></a>
<span class="sourceLineNo">185</span>  }<a name="line.185"></a>
<span class="sourceLineNo">186</span><a name="line.186"></a>
<span class="sourceLineNo">187</span>  private static class ImmediateCancelledFuture&lt;V&gt; extends ImmediateFuture&lt;V&gt; {<a name="line.187"></a>
<span class="sourceLineNo">188</span><a name="line.188"></a>
<span class="sourceLineNo">189</span>    private final CancellationException thrown;<a name="line.189"></a>
<span class="sourceLineNo">190</span><a name="line.190"></a>
<span class="sourceLineNo">191</span>    ImmediateCancelledFuture() {<a name="line.191"></a>
<span class="sourceLineNo">192</span>      this.thrown = new CancellationException("Immediate cancelled future.");<a name="line.192"></a>
<span class="sourceLineNo">193</span>    }<a name="line.193"></a>
<span class="sourceLineNo">194</span><a name="line.194"></a>
<span class="sourceLineNo">195</span>    @Override<a name="line.195"></a>
<span class="sourceLineNo">196</span>    public boolean isCancelled() {<a name="line.196"></a>
<span class="sourceLineNo">197</span>      return true;<a name="line.197"></a>
<span class="sourceLineNo">198</span>    }<a name="line.198"></a>
<span class="sourceLineNo">199</span><a name="line.199"></a>
<span class="sourceLineNo">200</span>    @Override<a name="line.200"></a>
<span class="sourceLineNo">201</span>    public V get() {<a name="line.201"></a>
<span class="sourceLineNo">202</span>      throw AbstractFuture.cancellationExceptionWithCause(<a name="line.202"></a>
<span class="sourceLineNo">203</span>          "Task was cancelled.", thrown);<a name="line.203"></a>
<span class="sourceLineNo">204</span>    }<a name="line.204"></a>
<span class="sourceLineNo">205</span>  }<a name="line.205"></a>
<span class="sourceLineNo">206</span><a name="line.206"></a>
<span class="sourceLineNo">207</span>  private static class ImmediateFailedCheckedFuture&lt;V, X extends Exception&gt;<a name="line.207"></a>
<span class="sourceLineNo">208</span>      extends ImmediateFuture&lt;V&gt; implements CheckedFuture&lt;V, X&gt; {<a name="line.208"></a>
<span class="sourceLineNo">209</span><a name="line.209"></a>
<span class="sourceLineNo">210</span>    private final X thrown;<a name="line.210"></a>
<span class="sourceLineNo">211</span><a name="line.211"></a>
<span class="sourceLineNo">212</span>    ImmediateFailedCheckedFuture(X thrown) {<a name="line.212"></a>
<span class="sourceLineNo">213</span>      this.thrown = thrown;<a name="line.213"></a>
<span class="sourceLineNo">214</span>    }<a name="line.214"></a>
<span class="sourceLineNo">215</span><a name="line.215"></a>
<span class="sourceLineNo">216</span>    @Override<a name="line.216"></a>
<span class="sourceLineNo">217</span>    public V get() throws ExecutionException {<a name="line.217"></a>
<span class="sourceLineNo">218</span>      throw new ExecutionException(thrown);<a name="line.218"></a>
<span class="sourceLineNo">219</span>    }<a name="line.219"></a>
<span class="sourceLineNo">220</span><a name="line.220"></a>
<span class="sourceLineNo">221</span>    @Override<a name="line.221"></a>
<span class="sourceLineNo">222</span>    public V checkedGet() throws X {<a name="line.222"></a>
<span class="sourceLineNo">223</span>      throw thrown;<a name="line.223"></a>
<span class="sourceLineNo">224</span>    }<a name="line.224"></a>
<span class="sourceLineNo">225</span><a name="line.225"></a>
<span class="sourceLineNo">226</span>    @Override<a name="line.226"></a>
<span class="sourceLineNo">227</span>    public V checkedGet(long timeout, TimeUnit unit) throws X {<a name="line.227"></a>
<span class="sourceLineNo">228</span>      checkNotNull(unit);<a name="line.228"></a>
<span class="sourceLineNo">229</span>      throw thrown;<a name="line.229"></a>
<span class="sourceLineNo">230</span>    }<a name="line.230"></a>
<span class="sourceLineNo">231</span>  }<a name="line.231"></a>
<span class="sourceLineNo">232</span><a name="line.232"></a>
<span class="sourceLineNo">233</span>  /**<a name="line.233"></a>
<span class="sourceLineNo">234</span>   * Creates a {@code ListenableFuture} which has its value set immediately upon<a name="line.234"></a>
<span class="sourceLineNo">235</span>   * construction. The getters just return the value. This {@code Future} can't<a name="line.235"></a>
<span class="sourceLineNo">236</span>   * be canceled or timed out and its {@code isDone()} method always returns<a name="line.236"></a>
<span class="sourceLineNo">237</span>   * {@code true}.<a name="line.237"></a>
<span class="sourceLineNo">238</span>   */<a name="line.238"></a>
<span class="sourceLineNo">239</span>  public static &lt;V&gt; ListenableFuture&lt;V&gt; immediateFuture(@Nullable V value) {<a name="line.239"></a>
<span class="sourceLineNo">240</span>    return new ImmediateSuccessfulFuture&lt;V&gt;(value);<a name="line.240"></a>
<span class="sourceLineNo">241</span>  }<a name="line.241"></a>
<span class="sourceLineNo">242</span><a name="line.242"></a>
<span class="sourceLineNo">243</span>  /**<a name="line.243"></a>
<span class="sourceLineNo">244</span>   * Returns a {@code CheckedFuture} which has its value set immediately upon<a name="line.244"></a>
<span class="sourceLineNo">245</span>   * construction.<a name="line.245"></a>
<span class="sourceLineNo">246</span>   *<a name="line.246"></a>
<span class="sourceLineNo">247</span>   * &lt;p&gt;The returned {@code Future} can't be cancelled, and its {@code isDone()}<a name="line.247"></a>
<span class="sourceLineNo">248</span>   * method always returns {@code true}. Calling {@code get()} or {@code<a name="line.248"></a>
<span class="sourceLineNo">249</span>   * checkedGet()} will immediately return the provided value.<a name="line.249"></a>
<span class="sourceLineNo">250</span>   */<a name="line.250"></a>
<span class="sourceLineNo">251</span>  public static &lt;V, X extends Exception&gt; CheckedFuture&lt;V, X&gt;<a name="line.251"></a>
<span class="sourceLineNo">252</span>      immediateCheckedFuture(@Nullable V value) {<a name="line.252"></a>
<span class="sourceLineNo">253</span>    return new ImmediateSuccessfulCheckedFuture&lt;V, X&gt;(value);<a name="line.253"></a>
<span class="sourceLineNo">254</span>  }<a name="line.254"></a>
<span class="sourceLineNo">255</span><a name="line.255"></a>
<span class="sourceLineNo">256</span>  /**<a name="line.256"></a>
<span class="sourceLineNo">257</span>   * Returns a {@code ListenableFuture} which has an exception set immediately<a name="line.257"></a>
<span class="sourceLineNo">258</span>   * upon construction.<a name="line.258"></a>
<span class="sourceLineNo">259</span>   *<a name="line.259"></a>
<span class="sourceLineNo">260</span>   * &lt;p&gt;The returned {@code Future} can't be cancelled, and its {@code isDone()}<a name="line.260"></a>
<span class="sourceLineNo">261</span>   * method always returns {@code true}. Calling {@code get()} will immediately<a name="line.261"></a>
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<span class="sourceLineNo">263</span>   * ExecutionException}.<a name="line.263"></a>
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<span class="sourceLineNo">265</span>  public static &lt;V&gt; ListenableFuture&lt;V&gt; immediateFailedFuture(<a name="line.265"></a>
<span class="sourceLineNo">266</span>      Throwable throwable) {<a name="line.266"></a>
<span class="sourceLineNo">267</span>    checkNotNull(throwable);<a name="line.267"></a>
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<span class="sourceLineNo">272</span>   * Creates a {@code ListenableFuture} which is cancelled immediately upon<a name="line.272"></a>
<span class="sourceLineNo">273</span>   * construction, so that {@code isCancelled()} always returns {@code true}.<a name="line.273"></a>
<span class="sourceLineNo">274</span>   *<a name="line.274"></a>
<span class="sourceLineNo">275</span>   * @since 14.0<a name="line.275"></a>
<span class="sourceLineNo">276</span>   */<a name="line.276"></a>
<span class="sourceLineNo">277</span>  public static &lt;V&gt; ListenableFuture&lt;V&gt; immediateCancelledFuture() {<a name="line.277"></a>
<span class="sourceLineNo">278</span>    return new ImmediateCancelledFuture&lt;V&gt;();<a name="line.278"></a>
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<span class="sourceLineNo">281</span>  /**<a name="line.281"></a>
<span class="sourceLineNo">282</span>   * Returns a {@code CheckedFuture} which has an exception set immediately upon<a name="line.282"></a>
<span class="sourceLineNo">283</span>   * construction.<a name="line.283"></a>
<span class="sourceLineNo">284</span>   *<a name="line.284"></a>
<span class="sourceLineNo">285</span>   * &lt;p&gt;The returned {@code Future} can't be cancelled, and its {@code isDone()}<a name="line.285"></a>
<span class="sourceLineNo">286</span>   * method always returns {@code true}. Calling {@code get()} will immediately<a name="line.286"></a>
<span class="sourceLineNo">287</span>   * throw the provided {@code Exception} wrapped in an {@code<a name="line.287"></a>
<span class="sourceLineNo">288</span>   * ExecutionException}, and calling {@code checkedGet()} will throw the<a name="line.288"></a>
<span class="sourceLineNo">289</span>   * provided exception itself.<a name="line.289"></a>
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<span class="sourceLineNo">292</span>      immediateFailedCheckedFuture(X exception) {<a name="line.292"></a>
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<span class="sourceLineNo">296</span><a name="line.296"></a>
<span class="sourceLineNo">297</span>  /**<a name="line.297"></a>
<span class="sourceLineNo">298</span>   * Returns a {@code Future} whose result is taken from the given primary<a name="line.298"></a>
<span class="sourceLineNo">299</span>   * {@code input} or, if the primary input fails, from the {@code Future}<a name="line.299"></a>
<span class="sourceLineNo">300</span>   * provided by the {@code fallback}. {@link FutureFallback#create} is not<a name="line.300"></a>
<span class="sourceLineNo">301</span>   * invoked until the primary input has failed, so if the primary input<a name="line.301"></a>
<span class="sourceLineNo">302</span>   * succeeds, it is never invoked. If, during the invocation of {@code<a name="line.302"></a>
<span class="sourceLineNo">303</span>   * fallback}, an exception is thrown, this exception is used as the result of<a name="line.303"></a>
<span class="sourceLineNo">304</span>   * the output {@code Future}.<a name="line.304"></a>
<span class="sourceLineNo">305</span>   *<a name="line.305"></a>
<span class="sourceLineNo">306</span>   * &lt;p&gt;Below is an example of a fallback that returns a default value if an<a name="line.306"></a>
<span class="sourceLineNo">307</span>   * exception occurs:<a name="line.307"></a>
<span class="sourceLineNo">308</span>   *<a name="line.308"></a>
<span class="sourceLineNo">309</span>   * &lt;pre&gt;   {@code<a name="line.309"></a>
<span class="sourceLineNo">310</span>   *   ListenableFuture&lt;Integer&gt; fetchCounterFuture = ...;<a name="line.310"></a>
<span class="sourceLineNo">311</span>   *<a name="line.311"></a>
<span class="sourceLineNo">312</span>   *   // Falling back to a zero counter in case an exception happens when<a name="line.312"></a>
<span class="sourceLineNo">313</span>   *   // processing the RPC to fetch counters.<a name="line.313"></a>
<span class="sourceLineNo">314</span>   *   ListenableFuture&lt;Integer&gt; faultTolerantFuture = Futures.withFallback(<a name="line.314"></a>
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<span class="sourceLineNo">316</span>   *         public ListenableFuture&lt;Integer&gt; create(Throwable t) {<a name="line.316"></a>
<span class="sourceLineNo">317</span>   *           // Returning "0" as the default for the counter when the<a name="line.317"></a>
<span class="sourceLineNo">318</span>   *           // exception happens.<a name="line.318"></a>
<span class="sourceLineNo">319</span>   *           return immediateFuture(0);<a name="line.319"></a>
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<span class="sourceLineNo">323</span>   *<a name="line.323"></a>
<span class="sourceLineNo">324</span>   * The fallback can also choose to propagate the original exception when<a name="line.324"></a>
<span class="sourceLineNo">325</span>   * desired:<a name="line.325"></a>
<span class="sourceLineNo">326</span>   *<a name="line.326"></a>
<span class="sourceLineNo">327</span>   * &lt;pre&gt;   {@code<a name="line.327"></a>
<span class="sourceLineNo">328</span>   *   ListenableFuture&lt;Integer&gt; fetchCounterFuture = ...;<a name="line.328"></a>
<span class="sourceLineNo">329</span>   *<a name="line.329"></a>
<span class="sourceLineNo">330</span>   *   // Falling back to a zero counter only in case the exception was a<a name="line.330"></a>
<span class="sourceLineNo">331</span>   *   // TimeoutException.<a name="line.331"></a>
<span class="sourceLineNo">332</span>   *   ListenableFuture&lt;Integer&gt; faultTolerantFuture = Futures.withFallback(<a name="line.332"></a>
<span class="sourceLineNo">333</span>   *       fetchCounterFuture, new FutureFallback&lt;Integer&gt;() {<a name="line.333"></a>
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<span class="sourceLineNo">338</span>   *           return immediateFailedFuture(t);<a name="line.338"></a>
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<span class="sourceLineNo">340</span>   *       });<a name="line.340"></a>
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<span class="sourceLineNo">342</span>   *<a name="line.342"></a>
<span class="sourceLineNo">343</span>   * Note: If the derived {@code Future} is slow or heavyweight to create<a name="line.343"></a>
<span class="sourceLineNo">344</span>   * (whether the {@code Future} itself is slow or heavyweight to complete is<a name="line.344"></a>
<span class="sourceLineNo">345</span>   * irrelevant), consider {@linkplain #withFallback(ListenableFuture,<a name="line.345"></a>
<span class="sourceLineNo">346</span>   * FutureFallback, Executor) supplying an executor}. If you do not supply an<a name="line.346"></a>
<span class="sourceLineNo">347</span>   * executor, {@code withFallback} will use {@link<a name="line.347"></a>
<span class="sourceLineNo">348</span>   * MoreExecutors#sameThreadExecutor sameThreadExecutor}, which carries some<a name="line.348"></a>
<span class="sourceLineNo">349</span>   * caveats for heavier operations. For example, the call to {@code<a name="line.349"></a>
<span class="sourceLineNo">350</span>   * fallback.create} may run on an unpredictable or undesirable thread:<a name="line.350"></a>
<span class="sourceLineNo">351</span>   *<a name="line.351"></a>
<span class="sourceLineNo">352</span>   * &lt;ul&gt;<a name="line.352"></a>
<span class="sourceLineNo">353</span>   * &lt;li&gt;If the input {@code Future} is done at the time {@code withFallback}<a name="line.353"></a>
<span class="sourceLineNo">354</span>   * is called, {@code withFallback} will call {@code fallback.create} inline.<a name="line.354"></a>
<span class="sourceLineNo">355</span>   * &lt;li&gt;If the input {@code Future} is not yet done, {@code withFallback} will<a name="line.355"></a>
<span class="sourceLineNo">356</span>   * schedule {@code fallback.create} to be run by the thread that completes<a name="line.356"></a>
<span class="sourceLineNo">357</span>   * the input {@code Future}, which may be an internal system thread such as<a name="line.357"></a>
<span class="sourceLineNo">358</span>   * an RPC network thread.<a name="line.358"></a>
<span class="sourceLineNo">359</span>   * &lt;/ul&gt;<a name="line.359"></a>
<span class="sourceLineNo">360</span>   *<a name="line.360"></a>
<span class="sourceLineNo">361</span>   * Also note that, regardless of which thread executes {@code<a name="line.361"></a>
<span class="sourceLineNo">362</span>   * fallback.create}, all other registered but unexecuted listeners are<a name="line.362"></a>
<span class="sourceLineNo">363</span>   * prevented from running during its execution, even if those listeners are<a name="line.363"></a>
<span class="sourceLineNo">364</span>   * to run in other executors.<a name="line.364"></a>
<span class="sourceLineNo">365</span>   *<a name="line.365"></a>
<span class="sourceLineNo">366</span>   * @param input the primary input {@code Future}<a name="line.366"></a>
<span class="sourceLineNo">367</span>   * @param fallback the {@link FutureFallback} implementation to be called if<a name="line.367"></a>
<span class="sourceLineNo">368</span>   *     {@code input} fails<a name="line.368"></a>
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<span class="sourceLineNo">371</span>      ListenableFuture&lt;? extends V&gt; input,<a name="line.371"></a>
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<span class="sourceLineNo">375</span><a name="line.375"></a>
<span class="sourceLineNo">376</span>  /**<a name="line.376"></a>
<span class="sourceLineNo">377</span>   * Returns a {@code Future} whose result is taken from the given primary<a name="line.377"></a>
<span class="sourceLineNo">378</span>   * {@code input} or, if the primary input fails, from the {@code Future}<a name="line.378"></a>
<span class="sourceLineNo">379</span>   * provided by the {@code fallback}. {@link FutureFallback#create} is not<a name="line.379"></a>
<span class="sourceLineNo">380</span>   * invoked until the primary input has failed, so if the primary input<a name="line.380"></a>
<span class="sourceLineNo">381</span>   * succeeds, it is never invoked. If, during the invocation of {@code<a name="line.381"></a>
<span class="sourceLineNo">382</span>   * fallback}, an exception is thrown, this exception is used as the result of<a name="line.382"></a>
<span class="sourceLineNo">383</span>   * the output {@code Future}.<a name="line.383"></a>
<span class="sourceLineNo">384</span>   *<a name="line.384"></a>
<span class="sourceLineNo">385</span>   * &lt;p&gt;Below is an example of a fallback that returns a default value if an<a name="line.385"></a>
<span class="sourceLineNo">386</span>   * exception occurs:<a name="line.386"></a>
<span class="sourceLineNo">387</span>   *<a name="line.387"></a>
<span class="sourceLineNo">388</span>   * &lt;pre&gt;   {@code<a name="line.388"></a>
<span class="sourceLineNo">389</span>   *   ListenableFuture&lt;Integer&gt; fetchCounterFuture = ...;<a name="line.389"></a>
<span class="sourceLineNo">390</span>   *<a name="line.390"></a>
<span class="sourceLineNo">391</span>   *   // Falling back to a zero counter in case an exception happens when<a name="line.391"></a>
<span class="sourceLineNo">392</span>   *   // processing the RPC to fetch counters.<a name="line.392"></a>
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<span class="sourceLineNo">395</span>   *         public ListenableFuture&lt;Integer&gt; create(Throwable t) {<a name="line.395"></a>
<span class="sourceLineNo">396</span>   *           // Returning "0" as the default for the counter when the<a name="line.396"></a>
<span class="sourceLineNo">397</span>   *           // exception happens.<a name="line.397"></a>
<span class="sourceLineNo">398</span>   *           return immediateFuture(0);<a name="line.398"></a>
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<span class="sourceLineNo">400</span>   *       }, sameThreadExecutor());<a name="line.400"></a>
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<span class="sourceLineNo">402</span>   *<a name="line.402"></a>
<span class="sourceLineNo">403</span>   * The fallback can also choose to propagate the original exception when<a name="line.403"></a>
<span class="sourceLineNo">404</span>   * desired:<a name="line.404"></a>
<span class="sourceLineNo">405</span>   *<a name="line.405"></a>
<span class="sourceLineNo">406</span>   * &lt;pre&gt;   {@code<a name="line.406"></a>
<span class="sourceLineNo">407</span>   *   ListenableFuture&lt;Integer&gt; fetchCounterFuture = ...;<a name="line.407"></a>
<span class="sourceLineNo">408</span>   *<a name="line.408"></a>
<span class="sourceLineNo">409</span>   *   // Falling back to a zero counter only in case the exception was a<a name="line.409"></a>
<span class="sourceLineNo">410</span>   *   // TimeoutException.<a name="line.410"></a>
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<span class="sourceLineNo">412</span>   *       fetchCounterFuture, new FutureFallback&lt;Integer&gt;() {<a name="line.412"></a>
<span class="sourceLineNo">413</span>   *         public ListenableFuture&lt;Integer&gt; create(Throwable t) {<a name="line.413"></a>
<span class="sourceLineNo">414</span>   *           if (t instanceof TimeoutException) {<a name="line.414"></a>
<span class="sourceLineNo">415</span>   *             return immediateFuture(0);<a name="line.415"></a>
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<span class="sourceLineNo">417</span>   *           return immediateFailedFuture(t);<a name="line.417"></a>
<span class="sourceLineNo">418</span>   *         }<a name="line.418"></a>
<span class="sourceLineNo">419</span>   *       }, sameThreadExecutor());<a name="line.419"></a>
<span class="sourceLineNo">420</span>   * }&lt;/pre&gt;<a name="line.420"></a>
<span class="sourceLineNo">421</span>   *<a name="line.421"></a>
<span class="sourceLineNo">422</span>   * When the execution of {@code fallback.create} is fast and lightweight<a name="line.422"></a>
<span class="sourceLineNo">423</span>   * (though the {@code Future} it returns need not meet these criteria),<a name="line.423"></a>
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<span class="sourceLineNo">425</span>   * omitting the executor} or explicitly specifying {@code<a name="line.425"></a>
<span class="sourceLineNo">426</span>   * sameThreadExecutor}. However, be aware of the caveats documented in the<a name="line.426"></a>
<span class="sourceLineNo">427</span>   * link above.<a name="line.427"></a>
<span class="sourceLineNo">428</span>   *<a name="line.428"></a>
<span class="sourceLineNo">429</span>   * @param input the primary input {@code Future}<a name="line.429"></a>
<span class="sourceLineNo">430</span>   * @param fallback the {@link FutureFallback} implementation to be called if<a name="line.430"></a>
<span class="sourceLineNo">431</span>   *     {@code input} fails<a name="line.431"></a>
<span class="sourceLineNo">432</span>   * @param executor the executor that runs {@code fallback} if {@code input}<a name="line.432"></a>
<span class="sourceLineNo">433</span>   *     fails<a name="line.433"></a>
<span class="sourceLineNo">434</span>   */<a name="line.434"></a>
<span class="sourceLineNo">435</span>  public static &lt;V&gt; ListenableFuture&lt;V&gt; withFallback(<a name="line.435"></a>
<span class="sourceLineNo">436</span>      ListenableFuture&lt;? extends V&gt; input,<a name="line.436"></a>
<span class="sourceLineNo">437</span>      FutureFallback&lt;? extends V&gt; fallback, Executor executor) {<a name="line.437"></a>
<span class="sourceLineNo">438</span>    checkNotNull(fallback);<a name="line.438"></a>
<span class="sourceLineNo">439</span>    return new FallbackFuture&lt;V&gt;(input, fallback, executor);<a name="line.439"></a>
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<span class="sourceLineNo">441</span><a name="line.441"></a>
<span class="sourceLineNo">442</span>  /**<a name="line.442"></a>
<span class="sourceLineNo">443</span>   * A future that falls back on a second, generated future, in case its<a name="line.443"></a>
<span class="sourceLineNo">444</span>   * original future fails.<a name="line.444"></a>
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<span class="sourceLineNo">446</span>  private static class FallbackFuture&lt;V&gt; extends AbstractFuture&lt;V&gt; {<a name="line.446"></a>
<span class="sourceLineNo">447</span><a name="line.447"></a>
<span class="sourceLineNo">448</span>    private volatile ListenableFuture&lt;? extends V&gt; running;<a name="line.448"></a>
<span class="sourceLineNo">449</span><a name="line.449"></a>
<span class="sourceLineNo">450</span>    FallbackFuture(ListenableFuture&lt;? extends V&gt; input,<a name="line.450"></a>
<span class="sourceLineNo">451</span>        final FutureFallback&lt;? extends V&gt; fallback,<a name="line.451"></a>
<span class="sourceLineNo">452</span>        final Executor executor) {<a name="line.452"></a>
<span class="sourceLineNo">453</span>      running = input;<a name="line.453"></a>
<span class="sourceLineNo">454</span>      addCallback(running, new FutureCallback&lt;V&gt;() {<a name="line.454"></a>
<span class="sourceLineNo">455</span>        @Override<a name="line.455"></a>
<span class="sourceLineNo">456</span>        public void onSuccess(V value) {<a name="line.456"></a>
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<span class="sourceLineNo">459</span><a name="line.459"></a>
<span class="sourceLineNo">460</span>        @Override<a name="line.460"></a>
<span class="sourceLineNo">461</span>        public void onFailure(Throwable t) {<a name="line.461"></a>
<span class="sourceLineNo">462</span>          if (isCancelled()) {<a name="line.462"></a>
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<span class="sourceLineNo">465</span>          try {<a name="line.465"></a>
<span class="sourceLineNo">466</span>            running = fallback.create(t);<a name="line.466"></a>
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<span class="sourceLineNo">468</span>              running.cancel(wasInterrupted());<a name="line.468"></a>
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<span class="sourceLineNo">471</span>            addCallback(running, new FutureCallback&lt;V&gt;() {<a name="line.471"></a>
<span class="sourceLineNo">472</span>              @Override<a name="line.472"></a>
<span class="sourceLineNo">473</span>              public void onSuccess(V value) {<a name="line.473"></a>
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<span class="sourceLineNo">476</span><a name="line.476"></a>
<span class="sourceLineNo">477</span>              @Override<a name="line.477"></a>
<span class="sourceLineNo">478</span>              public void onFailure(Throwable t) {<a name="line.478"></a>
<span class="sourceLineNo">479</span>                if (running.isCancelled()) {<a name="line.479"></a>
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<span class="sourceLineNo">482</span>                  setException(t);<a name="line.482"></a>
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<span class="sourceLineNo">485</span>            }, sameThreadExecutor());<a name="line.485"></a>
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<span class="sourceLineNo">487</span>            setException(e);<a name="line.487"></a>
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<span class="sourceLineNo">586</span>   * sync with that of the input future and that of the future returned by the<a name="line.586"></a>
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<span class="sourceLineNo">635</span>   * MoreExecutors#sameThreadExecutor sameThreadExecutor}, which carries some<a name="line.635"></a>
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</pre>
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